1. Field of the Invention
The present invention relates to steam turbine stationary blades.
2. Description of the Related Art
In the last stages of low pressure turbines and in one or two stages previous to the last stages, since pressure is typically very low, working fluid (steam) is in a state of the wet steam containing liquefied microscopic droplets of water. The water droplets contained in the working fluid stick to a surface of a stationary blade and combine with other water droplets to form a liquid film (drain) on the blade surface. After being withdrawn from the blade surface by the working fluid, the liquid film along with the working fluid flows down the flow passageway in a form of coarse droplets much larger than droplets of water. The coarse droplets, although more or less fine-grained by the working medium, continue to maintain a certain size and flow downward. Inertial force of the coarse droplets, however, does not allow them to change their direction of flow along the flow passageway as suddenly as the working fluid can. For this reason, the coarse droplets are likely to rapidly collide against a moving blade present downstream in the flow direction of the coarse droplets, thus to cause erosion of the moving blade surface or to impede rotation of the moving blade, and to result in moisture loss.
To reduce erosion, generally it is most effective to remove the liquid film formed on the surface of the stationary blade. In contrast, JP-2014-25443-A, for example, proposes providing a slot in a trailing edge (tail side) of a stationary blade and drawing a liquid film into a hollow region of the blade via the slot.